I. Field of the Invention
The present invention relates to the field of molding and molded parts and in particular the field of coating molded parts. More particularly the present invention relates to the field of mold coating molded parts made from thermoplastic compounds to produce a class A finish on the surfaces of the part.
II. Prior Art Statement
The need for a class A finish on injection molded and structural foam parts made from synthetic resinous materials has long been known. Normally parts made from such materials, especially thermoplastic materials have pores and cracks which require filling and hand finishing to produce a surface that can be painted or otherwise finished. One method for mold coating an injection molded or structural foam part to achieve a satisfactory finish includes spraying a coating on the inside of the mold on the surfaces where the improved finish is desired before closing the mold. The plastic material is then injected into the mold. This method is unsatisfactory in that the injected material tends to wash away the coating at the point of injection. Another alternative is to merely secondarily paint the surface.
U.S. Pat. No. 4,081,578 disclosed a method for mold coating sheet molded compound parts by opening the mold after the part has been formed. A measured amount of coating material is then injected into the mold in the space between the surface of the mold and the surface of the part. The mold is then closed to distribute the coating material over the part. The coating material is then cured. The mold is, then, opened and the part ejected from the mold. This process is capable of producing a class A finish on the part. However, when the mold is opened, air is allowed to enter the space between the surface of the mold and the surface of the part. The injecting of air into the mold introduces moisture and debris into the mold which can introduce flaws into the resulting surface finish. Furthermore the presence of moisture tends to interact with the coating material causing blemishes and a tendency for the coating to chip and peel.
German Pat. No. 2,442,227 and English Pat. No. 1,457,935 are related to the aforementioned U.S. Patent. These patents constitute the entire prior art known to the inventors.